FIGURE 2.

Chemical Structures of iTRAQ, TMT, and TMTPro. Each molecule consists of a reporter group, a mass balance group, and a peptide‐reactive group. iTRAQ contains a distribution of ¹³C, ¹⁵N, and ¹⁸O isotopes across the balance and reporter groups, while TMT and TMTPro consist of ¹³C and ¹⁵N only. iTRAQ consists of a N‐methylpiperazine reporter group, TMT with a dimethylpiperidine reporter and TMTPro contains an isobutyl‐proline reporter ion. Each tag carries an NHS reactive group, while mass normalization groups vary across each structure